WIN TKR CYCLE AND WINTKU PAUSE 3^73 



\Vint?:k Pause 



In the following ta!)le are given tiie number of pause and non-pause birds 

 by years, togetiier with tlie percentage of birds in tlie pause class. 



Year Non-Pause Pause Total % Witli Pause 



Birds Birds 



1916 120 15«) 279 56.99 



1917 153 239 392 60.97 



1918 115 248 363 68.32 



1919 59 109 168 64.88 



1920 48 133 181 73.48 



1921 276 175 451 38.80 



1922 201 376 577 65.16 



1923 109 353 462 76.41 



1924 160 340 500 68.00 



Tiie average length of j)ause for those birds pausing is as follows: 



1916 flock 29.46 days 



1921 flock 19.23 days 



1924 flock 32.97 days 



6. Correlation Between Length of Winter Cycle and Length of Winter Pause. 



The range in cycle length was found to be from 5 days to 175 days. The 

 class interval used was 10 days. Since winter cycle and winter pause are 

 complementary to each other, it is important to discover their possible rela- 

 tion to each other. The coefficient of correlation will illustrate any tendency 

 for length of winter cycle and length of winter pause to move in the same or 

 in opposite directions. Such information will make clearer their physiological 

 relationships and possible genetic linkage. 



Xuiiibcr of birds ...... 



Mean length of winter cycle 



Length of winter cycle standard deviation . 



Mean length of winter pause 



Length of winter pause standard deviation 



Coefficient of correlation .... 



Regression winter cycle on pause 

 Regression pause on winter cycle 



2078 



52.26 

 ±3t.23 



31.91 

 ±21.68 



—.1385 ± .014.5 



—.219 



—.088 



The ler>gth of winter cycle as measured in the.se studies is sul)ject to wide 

 fluctuation as indicated by the relative magnitude of the mean and its stand- 

 ard deviation. Such fluctuations are to be anticipated in a population highly 

 variable for the seven pairs of inherited factors concerned in winter produc- 

 tion, subjected to uncontrollable variation in environmental influences. The 

 fact should be observed, however, that the mean length of winter cycle is 

 about 63 per cent greater than the mean length of pause. 



A small negative correlation coefficient indicates a very slight tendency for 

 long-cycle birds to pause for a shorter period than do short-cycle birds. This 



